The House January 6 select committee on Thursday asked former Republican House speaker Newt Gingrich to testify about his repeated contacts with White House aides in Donald Trump’s efforts to overturn the 2020 election results, even in the evening after the Capitol attack had taken place.

The request to Gingrich was for voluntary cooperation – though the select committee showed it now appears to believe he was involved in a potential conspiracy planned ahead of time to lay the groundwork that would lead to reversing Trump’s defeat on January 6.

Congressman Bennie Thompson, the committee chair, said in a letter to Gingrich that investigators were interested in him counseling Trump aides to make TV ads about debunked election fraud conspiracies to pressure state legislators into decertifying Biden electors.

The letter detailed that it had communications that showed he tried to liaise with former Trump White House chief of staff Mark Meadows and former Trump White House counsel Pat Cipollone about the fake elector scheme, asking whether anyone was coordinating Trump slates to Congress so that he could be declared the winner.

The select committee noted that Gingrich then furthered that effort as he emailed Meadows at 10.42pm on January 6 – hours after the Capitol attack had already largely concluded and Congress was preparing to confirm Biden’s win – asking whether there were “letters from state legislators about decertifying electors”.

“Surprisingly, the attack on Congress and the activities prescribed by the Constitution did not even pause your relentless pursuit. On the evening of January 6, you continued to push efforts to overturn the election results,” the letter said.

The select committee stopped short of issuing a subpoena to Gingrich, but also asked him to preserve his communications with Trump, the White House and the Trump legal team led by Rudy Giuliani and John Eastman, as well as anyone else connected to January 6.